Fix some problems with config form (when switching themes)
Add Chicago theme

This isn't very parameterizable, but I think it is a good test case for
the themes system.  It doesn't look perfect; some elements, like the login
box, needed coaxing to work alongside Bootstrap.
Clear current theme before loading a new one

This is necessary in case the themes you are switching between use a
different set of template overrides.
Fix ThemeController.list_filenames()
Clear TemplateOverride cache when changing theme
Initial commit of MIT theme for generic templates

When loaded, this theme mimics the MIT ESP site.  It does so without using
images - the rounded corners, tabs, buttons, etc. are made using CSS only,
which is parameterized.

Some work will still be needed to parameterize this for use by other
chapters, and to make appearance degrade gracefully on less modern
browsers that don't support things like border-radius.
Add error logging to LESS compile
Make NavStructureWidget globally available

I think some more themes will make of it (in some form) in the future.
Make MIT theme parameterized

This brings in the NavStructureWidget from the generic2 theme to specify
the tab structure.  This is slightly different than the original template
overrides in that no tabs will be displayed if you're outside the areas
defined by the top-level tabs.  I invite suggestions for fixes for this.
Make THEME_DEBUG False by default to suppress print statements
Add CDN_ADDRESS setting and use it in templates for Bootstrap etc.

This is sort of like Django's MEDIA_URL except for the CDN.  Note that the
CDN should only be used for files that are exactly the same across all of
our sites.  Also, I changed the URL to avoid using our hostname; Amazon
doesn't have the ability to serve our HTTPS certificate, so we just use
their hostname and their certificate.
Fix bug in render_to_response() so settings are always in context
Merge, rather than replace, theme settings on save

This is so that you can switch back and forth between themes and the
system won't forget the settings that are used by some themes and not
others.
Add default path for icon images on CDN
Fix first-time run bug in ThemeController.clear_theme()